The class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon has been known for some time. Nozaki, e.g., U.S. Pat. No. 3,694,412, produced such polymers in the presence of arylphosphine complexes of palladium moieties and certain inert solvents. More recently, the production of the linear alternating polymers, now known as polyketones or polyketone polymers, is illustrated by a number of published European Patent Applications including Nos. 121,965, 181,014, 213,671 and 257,663. The processes involve the use of a catalyst composition formed from a compound of palladium, cobalt or nickel, the anion of a strong non-hydrohalogenic acid and a bidentate ligand of phosphorus, arsenic, antimony or nitrogen. Although the scope of the polymerization process is extensive, and without wishing to be limited, a preferred catalyst composition is formed from a compound of palladium, the anion of a non-hydrohalogenic acid having a pKa below 2 and a bidentate ligand of phosphorus.
Although the choice of each catalyst composition precursor has an important effect upon the nature of the catalyst composition, the choice of ligand seems to be particularly important. The relevant above published applications illustrate the use of tetraalkyl diphosphines or tetraaryl diphosphines wherein the aryl groups are hydrocarbon or are substituted hydrocarbon where a substituent group is polar, particularly alkoxy. In the disclosure of published European Patent Application EP 305012, good results are obtained when the diphosphine ligand from which the catalyst composition is of the general formula (XX'P).sub.2 Y wherein X is an aromatic group, X' is a heteroaromatic group and Y is a divalent linking group. It would be of advantage, however, to provide additional bidentate phosphine ligands which give even better results when employed as part of a catalyst composition used to catalyze the production of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon.